In general, in the United States, the Federal Communications Commission (FCC) regulates wireless transmission frequency bands. For years, broadcasters have been licensed by the FCC for analog television channel transmission via licensed frequency bands within a frequency range from approximately 54 MHz to approximately 700 MHz. Generally, within a range of approximately 100 kilometers from a broadcast tower, unlicensed television transmissions are prohibited.
Recognizing that the UHF TV band (roughly 500 to 700 MHz) may be useful for consumer-oriented applications, the FCC is seeking to allow unlicensed users (such as individual consumers) to use these frequencies in ‘whitespace’ areas, that is, areas where individual TV channels are unused by licensed operators such as TV broadcasters or areas that do not receive UHF TV band signals.
However, there are potential problems presented by unlicensed UH whitespace applications. For example, the long propagation range of UHF frequencies opens the possibility that an unlicensed user, operating outside the nominal coverage area of a TV station, could nonetheless cause interference to a TV watcher within the station's coverage area many miles away by transmitting data in the same frequency band as a channel being viewed by the TV watcher. This may be a particular problem for mobile devices (i.e. portable devices, such as laptop-type portable local area network (LAN) devices) since users may take their mobile devices into locations within or near a station's coverage area.